This invention relates to a hydrogen storage alloy electrode, in particular to a magnesium alloy based active material.
It is well know in the art that there are many kinds of hydrogen storage alloy active materials, such as rare earth system (LaNi.sub.5 etc), titanium system (TiNi etc), zirconium system (ZrMn.sub.2 etc), calcium system (CaNi etc), and magnesium system (Mg.sub.2 Ni etc). The rare earth system and titanium system are studied the most and applied to alkali batteries (concentrating mainly on the sealed cylindrical batteries used for the electricity supply of portable equipment). The next most studied systems are zirconium system and calcium system. Few reports of the magnesium system can be found.
Nevertheless, further requirements are proposed for the performances of alkali batteries for today's large scale electrical equipment, especially electrically operated vehicles, wherein one of the main technical indexes is high energy density. Because the weights of the elements present in alloys of rare earth system and titanium system are heavy, improvement of the energy density of alkali batteries assembled with electrodes prepared from these materials is limited. Furthermore the cost of the alloys of rare earth system and titanium system is expensive, so that their application to alkali batteries for large scale electrical equipment is also limited. The most ideal hydrogen storage alloy applied in this respect is the magnesium system alloy. However, hydrogen is relatively stable in the magnesium base, and can only be absorbed under high pressure and desorbed at high temperature. The magnesium based alloy developed at present can only absorb hydrogen under 3.about.10 atm pressure and desorb hydrogen at 300.degree. C. temperature. See Seiler, S. et al., in J. Less--Common Met. 73, 193 (1980). This magnesium based alloy, however cannot be applied under normal conditions.